ASYNC Interface

Name

ASYNC -- Interface Type "ASYNC".

Description

The ASYNC interface type specifies an asynchronous character-by character interface, such as RS232 or a pseudo-TTY.

It is so-called because individual characters are sent and received asynchronously, either singly or in random sized bunches, rather than in strict synchronism with a clock signal.

In XRPi this usually means USB-to-Serial adaptors which appear as /dev/ttyUSB0 etc.

A typical ASYNC interface would be defined thus:

	INTERFACE=1
		TYPE=ASYNC
		ID=Multidrop KISS TNCs
		COM=/dev/ttyUSB1
		SPEED=9600
		PROTOCOL=KISS
		KISSOPTIONS=POLLED,CHECKSUM,ACKMODE
		MTU=256
		FLOW=0
	ENDINTERFACE

TYPE, COM, SPEED, PROTOCOL and MTU are mandatory.

ID is an optional plain text string which identifies the interface on various displays. Keep it concise. 20 characters max.
COM is the serial device name, e.g. "/dev/tty0". COM=0 is a "dummy" device which reads and writes nothing. It can be used to "park" interfaces when not in use.
SPEED is the baud rate used on the interface. Don't include a comma, e.g use "9600" not "9,600". The range of supported baud rates depends on the device.

PROTOCOL is the protocol to use on the interface:

	ASCII    - Remote consoles (TTY)
	KISS     - For driving KISS TNCs or wired links.
	MODEM    - Hayes compatible PSTN modem.
	NETROM   - Netrom backend serial link.
	PPP      - Point to Point Protocol (TCP/IP over RS232)
	SLIP     - Serial Line Interface Protocol  (TCP/IP over RS232)
	TNC2     - TNC2 emulation.

MTU is the "Maximum Transmission Unit". This specifies the maximum size for the data portion of an IP packet transmitted on the interface.
Datagrams are sized or fragmented according to the MTU of the interface on which they are transmitted.
XRPi allows MTU's up to 1500 bytes, but setting MTU over 256 is not recommended on AX25 ports, because the buffer size on TNC-based nodes is usually only big enough for a 256-byte data field.

FLOW optionally specifies the flow control options:

	0 = No flow control
	1 = Hardware (RTS/CTS) flow control
	2 = Software (XON/XOFF) flow control (TTY link only)
	3 = Hardware AND software flow control

If not specified, flow control defaults to NONE. Don't use Xon/Xoff with KISS!.

KISSOPTIONS are special options for the KISS protocol only:

	NONE     - Plain KISS (most TNC's use this) (default)

	POLLED   - For TNCs which send only when polled.

	CHECKSUM - Packets are protected by checksum.  You can
                   only use this option if your TNC supports it.

	ACKMODE  - For TNC's which inform XRPi when a
                   frame has been transmitted on air.

	SLAVE    - XRPi will act like a polled KISS TNC,
                   sending only when commanded to do so.

POLLED and SLAVE are mutually exclusive. BPQKISS eproms require POLLED and CHECKSUM, but their use of ACKMODE is optional.

See also

IFACES -- Interfaces.
PORTS -- Ports.
XROUTER.CFG(8) -- Main Configuration File.